# 53BP1-RIF1 and DNA-PKcs show distinct genetic interactions with diverse chromosomal break repair outcomes

## TL;DR

This study explores how 53BP1-RIF1 and DNA-PKcs interact during DNA repair, revealing distinct roles in influencing repair outcomes.

## Contribution

The paper identifies distinct genetic interactions between 53BP1-RIF1 and DNA-PKcs in DNA repair pathways.

## Key findings

- Loss of 53BP1 alone does not affect blunt DSB NHEJ but reduces repair when combined with DNA-PKcs disruption.
- 53BP1-RIF1 and DNA-PKcs function in the same pathway to suppress microhomology deletions.
- DNA-PKcs kinase inhibition increases radiosensitivity and homology-directed repair without additive effects from 53BP1 loss.

## Abstract

53BP1 accumulates at DNA double strand breaks (DSBs) and is implicated in non-homologous end joining (NHEJ), but the genetic interplay of 53BP1 with the NHEJ pathway (e.g., DNA-PKcs) is poorly understood. We examine blunt DSB NHEJ of Cas9 DSBs, which is dependent on core NHEJ factors, and find that loss of 53BP1 does not affect such repair but causes a reduction when combined with DNA-PKcs disruption. In contrast, disrupting 53BP1 and DNA-PKcs, alone and together, has similar effects on the type of deletion mutation (increase in microhomology deletions). We find similar effects with RIF1, such that 53BP1-RIF1 appear to play a backup role for DNA-PKcs during blunt DSB NHEJ, but function in the same pathway to suppress microhomology deletions. Finally, DNA-PKcs kinase inhibition causes increased radiosensitivity and homology-directed repair that is not additive with loss of 53BP1. Altogether, 53BP1-RIF1 and DNA-PKcs show distinct genetic interactions with diverse DSB repair outcomes.

DNA double strand breaks can be repaired by several pathways leading to different genetic outcomes. Here, the authors define the interplay between the DNA damage response factors 53BP1-RIF1 and core non-homologous end joining factors on diverse repair outcomes.